Child With Joint And Muscle Pain, Swollen Glands, Itchy Rash, Rapid Pulse And Stretch Marks. Underlying Causing?

Question: Hi, my daughter is nearly 13 years old of average weight and height. She has been suffering for over a year now with joint & muscle pain and fatigue. Gradually she is getting worse and more symptoms are appearing. Swollen glands that come and go, itchy rashes that aren't like her ezcema, rapid pulse rate around 130 some weeks and then down to 97 other weeks, pain when breathing in she says it feels like cold air, she has got alot of purple,red stretch marks over the hips and thighs, but she isn't a big girl. She struggles swallowing her saliva. Sweats during the night but seems to be from her shoulders upwards, her hair is normally wet in the morning. She becomes out of breath after running up the stairs, she used to be extremely fit, but now she is struggling with her dancing and struggling to keep up with her friends. She is barely at school and hardly sees friends as she is always unwell. I look at photos from a year ago and I see how pale she has become and how dark under the eyes. As a parent I am worried sick, I feel she has some hormone problem but don't know what. She's had the routine blood tests and a thyroid test and are ok. Thanks for your help